Method for preparing a pearlescent pigment by coating metal oxides on the synthesized mica

ABSTRACT

Disclosed is a method for preparing a pearlescent pigment by coating metal oxides on the synthesized mica, involving the steps of grinding the synthesized mica by agitating the mica with water in a water mixer to a particle size between 100 and 500 μm and separating the mica, dispersing the separated particles of the synthesized mica in water and adding acid thereto to adjust pH between 1 and 4, adding the metal oxide precursors and a basic aqueous solution thereto while maintaining said pH range until the desired color is attained, and thereby forming at least one hydrous metal oxide layer on the particles of the synthesized mica, and filtering, water-washing, drying and calcining the synthesized mica coated with the metal oxide layer. The method may further involve the step of further pulverizing the synthesized mica roughly ground in a water mixer by using a conventional wet pulverizer so that less than 100 μm of the synthesized mica may be used as a base material. The suitable surfactants can be used in a water mixer as well as a conventional wet pulverizer. The pearlescent pigment prepared according to the present invention has excellent luster and chroma, since a coating layer of metal oxides is smooth and the dispersibility of the particles is excellent.

TECHNICAL FIELD

The preset invention relates to a method for preparing a pearlescentpigment, more specifically a method for preparing a pearlescent pigmenthaving excellent luster and chroma, comprising coating metal oxides suchas titanium dioxide, iron oxide and the like on the pulverizedsynthesized mica as a base material, characterized by modifying agrinding method of synthesized mica to improve the surface propertythereof and/or adding suitable surfactants to the pigment to improve adispersibility of the particles.

PRIOR ART

Since the origin era of mankind, they have sought various natural orsynthetic pigments or dyes to express their own beauty. Among them, apearlescent pigment has been widely used, because it has the inherentbeautiful color of its own contrary to other general pigments or dyes. Ageneral red pigment or dye expresses a red color in any visual angle. Onthe other hand, the pearlescent pigment expresses double or multiplecolors depending on visual angle on account of an angular difference,which occurs when a portion of light permeating the pearlescent pigmentis reflected and the other portion of light is refracted. Thisphenomenon is observed in a natural pearl, a fish scale, a clamshell, abird's feather, or butterfly's wing and the like. In the past, there wasused a guanine taken from the scales of fishes such as a herring and ahairtail in order to realize the pearlescent luster. However, sincethese natural resources cannot fulfil the demands of the pearlescentpigment, intensive studies on synthesis of pearlescent pigments havebeen in progress.

Representative examples of the synthesized pearlescent pigments includemica pigments coated with a lead carbonate, a BiOCl or titanium dioxide(TiO₂), but the pigments based on Al₂O₃, SiO₂, glass flake and the likehave been recently developed. Especially, the most commercially andwidely used pearlescent pigment is the mica pigment coated with titaniumdioxide which employs high refractivity of titanium dioxide. As a basematerial such as mica is coated with metal oxides or mixture thereofhaving high refractive index in a form of single or multiple layers, aninterface between two-layered media having different refractive indexpermits a visible light to partially reflect and transmit. As the lightbeams refracted or transmitted at the interface recombine constructivelyor destructively to enhance the intensity only for a certainwavelengths, the color corresponding to such wavelengths intensified ata reflective angle is observed. The said titanium dioxide-coated mica isadvantageous in that it is excellent in weatherproof property, chemicalresistance and physical property, is able to show diverse colorsdepending on the kind of the coated metal compound or dye and thecoating thickness, and is able to control its particle size to accord acertain use by a grinding/separating process. In addition, the saidpigment is also advantageous in that it is widely applied to automobilecoating, cosmetics, wall paper, floor materials, plasticextrusion/injection, synthesized leather, printing ink, paint and thelike. However, when natural mica is employed as a base material, therehappens a problem that its final product has no uniform quality due todifferent iron contents, hardness, impurities and the like, andexpresses yellowish color.

To solve the said problems, a technology to use the synthesized mica asa base material of the pearlescent pigment has been developed. However,when the synthesized mica is used to prepare a pearlescent pigment, thepearlescent pigment has to maintain the merit of the synthesized micaitself as well as has to exhibit more excellent luster and chroma thanthe natural mica-produced pigment. When a pearlescent pigment isprepared with a synthesized mica by a conventional wet pulverizingmethod as disclosed in U.S. Pat. No. 6,056,815, the luster and chroma ofthe pearlescent pigment deteriorate since the mica is ground by directfriction between the roller and the bottom surface to impair the surfaceof the mica. In other words, when the surface of the synthesized mica isnot partially smooth and uniform, the level of luster and chromarequired for the pearlescent pigment cannot be attained because of lightscattering. Further, when a metal oxide coating is not intensely boundon a base material, luster or chroma is deteriorated. For the reason, itis assumed that the heat generated by friction transforms the interfaceof the base material to lead a deterioration of binding between metaloxide and base material, and results in partially peeling the coating onaccount of external physical force.

U.S. Pat. No. 5,741,355 to Yamamoto et al discloses a pearlescentpigment wherein the average refractive index of the synthesized mica isnot more than 1.58, the surface of synthesized mica particles issmoothened and made flaky, the iron content in the synthetic mica is notmore than 1.0% by weight and a pearl parameter given by specific volumeand powder luster value of the synthesized mica is not less than 10. The'355 patent shows that fine powder of synthetic mica is added by atleast 1% or more to the melt of synthetic mica during synthesis bymelting of synthesized mica and is solidified and crystallized, suchcrystallized mass of synthetic mica is pulverized, or the meltedsubstance as taken out through the perforation of the shell iscrystallized in the heat insulating case and pulverized, in case thatthe synthetic mica is pulverized to particle size of 100 μm or smallerusing hammer mill, roll mill, ball mill, etc., addition of highviscosity medium makes the synthetic mica flaky and thereby smootheningthe surface of the mica. However, '355 patent has a problem that itrequires an additional process to obtain the particles of the syntheticmica in such shape as shown in the patent, and thereby makes the processcomplicate and economically disadvantageous.

In the preparation of the pearlescent pigment, it is also required thatthe interface of base material should be activated so as to prevent thesmall particles of the synthesized mica from being agglomerated to thelarge particles or each other and that the metal oxide should beadsorbed onto the synthesized mica in a smooth and uniform form. Whenthe metal oxide is not adsorbed onto the interface of base material, butagglomerated each other, the surface of the final product is rough orthe metal oxide is not bound to the base material and form particles bythemselves, and thereby deteriorate the luster and chroma of thepigment.

The present inventors have fervently studied for solving said problems.As a result, they have found that the surface of the synthesized mica ismaintained smoothly enough for coating metal oxides thereon in case thatthe synthesized mica is ground to a pulverized powder by a water mixerrather than a conventional wet grinding means. In addition, the presentinventors have developed a pearlescent pigment having an excellentluster and chroma by adding a suitable surfactant to the dispersion ofthe ground synthesized mica to uniformly disperse the synthesized micaparticles and to uniformly adsorb the hydrous metal oxide onto thesurface of the base material.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a pearlescentpigment having excellent luster and chroma or color saturation bykeeping the surface of the synthesized mica used as a base materialsmooth during the grinding step thereof.

It is another object of the present invention to provide a pearlescentpigment in which superior dispersibility of particles can be obtained byadding surfactants prior to coating metal oxides on the synthesizedmica.

It is still another object of the present invention to provide apearlescent pigment, which is excellent in weatherproof, chemicalresistance and physical properties and is able to exhibit various colorsdepending on the species of metal oxides or coating thickness.

It is still another object of the present invention to provide apearlescent pigment prepared in accordance with the method of thepresent invention.

Said objects can be achieved according to the present invention asexplained hereinafter. The present invention will be explained in detailas follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects, and other features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the drawings, in which:

FIG. 1 is a cross sectional view of a water mixer having a pitchpaddle-typed agitator structure used for grinding the synthesized micaaccording to the present invention;

FIG. 2 is an electromicroscopic photograph showing the surface ofpearlescent pigment particles prepared in Example 4; and

FIGS. 3 and 4 are electromicroscopic photographs showing the surface ofpearlescent pigment particles wherein titanium dioxide coating layer isformed on the synthesized mica ground by a conventional wet pulverizer.

BEST MODE FOR CARRYING OUT THE INVENTION

In the first embodiment of the present invention, there provides amethod for preparing the pearlescent pigments by coating metal oxides onthe synthesized mica, comprising the steps of:

(1) grinding the synthesized mica by agitating the mica with water in awater mixer to a particle size between 100 and 500 μm and separating themica;

(2) dispersing the separated particles of the synthesized mica in waterand adding acid thereto to adjust pH between 1 and 4;

(3) adding the metal oxide precursors and the basic aqueous solution tothe dispersion while maintaining said pH range until the desired coloris attained, and thereby forming at least one hydrous metal oxideslayers on the particles of the synthesized mica; and

(4) filtering, water-washing, drying and calcining the synthesized micacoated with the metal oxides layers.

Said method may comprises an additional step of further pulverizing thesynthesized mica roughly ground in a water mixer in the step (1) using aconventional wet pulverizer so that 100 μm or less of the synthesizedmica may be used as a base material.

In the second embodiment of the present invention, there provides amethod for preparing pearlescent pigments by coating metal oxides on thesynthesized mica, comprising the steps of:

(1) grinding the synthesized mica by agitating the mica with water in awet pulverizer to a particle size between 5 and 500 μm and separatingthe mica;

(2) dispersing the separated particles of the synthesized mica in waterand adding 0.0001 to 1.0% by weight of cationic, anionic, nonionic oramphionic surfactant thereto;

(3) adding acid to the dispersion containing the surfactant to adjust pHbetween 1 and 4;

(4) adding the metal oxide precursors and the basic aqueous solutionthereto while maintaining said pH range until the desired color isattained, and thereby forming at least one hydrous metal oxides layerson the particles of the synthesized mica; and

(5) filtering, water-washing, drying and calcining the synthesized micacoated with the metal oxides layers.

The pearlescent pigments prepared in accordance with the presentinvention have excellent luster and chroma or color saturation, becausethe synthesized mica mass produced by a conventional method is ground bya water mixer without damage of their surfaces, and a suitablesurfactant is added prior to the coating process of metal oxides thereonwhich is carried out separately or together with said grinding stepthereby the coated particles do not agglomerate each other and the metaloxides are uniformly adsorbed/bound on the surfaces of the synthesizedmica used as a base material.

In the present invention, the synthesized mica used as a base materialfor metal oxides layers is produced by a conventional resistance meltingmethod. Since the synthesized mica mass produced by the above methodhave about 1 to 10 cm of particle size, further pulverization is carriedout to obtain suitable particle sizes for grinding in the water mixer.

According to the present invention, it is required that it should beground in a size of 5 to 500 μm to be used for preparing a pearlescentpigment.

FIG. 1 is a cross sectional view showing a water mixer having a pitchedpaddle-typed agitator, which is used for grinding the synthesized micain accordance with the present invention.

In grinding the synthesized mica, water and the synthesized mica areintroduced in the water mixer in a weight ratio of 10:1 to 1:1, agitatedat the revolution speed of 100 to 1000 rpm for 0.5 to 2 hours to giveparticles of the synthesized mica, preferably in the form of flake,having particle size between 100 and 500 μm. The obtained synthesizedmica is suitable for a base material of pearlescent pigment, becausewater serves as a buffer not to substantially impair the surface of theparticles and easily soaks friction heat when the agitator paddles arecollided with the particles of the synthesized mica in the water mixer.A water mixer with pitched paddle-typed agitator is preferably used.However, since it is substantially impossible to grind the synthesizedmica in a particle size of 100 μm or less with a water mixer, it may beadditionally ground in a conventional wet pulverizer to obtain smallerparticle size of about 5 to 100 μm. A preferable example of such a wetpulverizer is an edge runner mill, which grinds the synthesized mica bya friction between a rotating roller and horizontal disc. As above,double grinding can make the surfaces of the particles much smoothercompared with the single grinding using only conventional wetpulverizer.

The particles of the pulverized mica are preferable subjected toseparation to give a narrow distribution of particle size, because theparticle size of pearlescent pigment prepared in the present inventionis altered depending on the use of the pigment, and the uniform particlesize enhances luster of the mica.

According to the present invention, the representative examples of themetal oxide layer coated on the particles of the synthesized mica aretitanium dioxide (TiO₂) layer, iron oxide (Fe₂O₃) layer, or combinationthereof. The layer mixed or combined with the ocher metal oxide, or theadditional metal oxide layer on the titanium dioxide layer and/or ironoxide layer may be formed for the purpose of changing the crystallinestructure of a coating layer to improve luster, preventing discolorationor exhibiting more diverse colors. The examples of the metal oxidesforming one layer together with the main metal oxides or the additionallayer include tin dioxide (SnO₂), zirconium dioxide (ZrO₂), silicondioxide (SiO₂), aluminum oxide (Al₂O₃), magnesium oxide (MgO), manganesedioxide (MnO₂) and the mixture thereof. Especially, the employment oftin dioxide has an advantage that the anatase structure of titaniumdioxide(TiO₂) coating layer is able to be changed to a rutile structureby precoating the surface of the synthesized mica with a thin layer ofthe hydrous tin dioxide (SnO₂) as disclosed in U.S. Pat. Nos. 4,038,099and 4,086,100 to improve luster and weatherproof property. It ispreferable that other assistant metal oxides than tin dioxide form onecoating layer together with a main metal oxide, or a mixture of the mainmetal oxide and tin dioxide.

According to the present invention, the contents of the coating layermay be preferably about 5 to 60% by weight depending on the desiredcolors and luster, and for improving weatherproof property. As thethickness of the layer sets thicker, the colors of silver, gold, red,purple, blue and green exhibit in order. In case that multiple coatinglayers are formed, for example, forming the second coating layerfollowing the first coating layer, the colors of silver, gold, red,purple, blue and green repeatedly exhibit in order. In addition to thisforming of multiple structures, the calcined pigments may be re-coatedwith the metal oxides such as chromium, zirconium, aluminum, or may betreated with silane in order to exhibit diverse colors or renderadditional weatherproof property. Even though forming the multi-coatinglayer, the whole content of the metal oxides coated on the synthesizedmica is preferably 5 to 80% by weight because too thick coating layer isliable to be peeled off the base material.

The method for preparing the pearlescent pigment is described hereafter.

At first, it is preferable that the particles of the synthesized micaare dispersed in water in an amount of about 5 to 15% by weight. It ispreferable to use the deionized water, if possible, to prevent thedisturbance of adsorption by ion. After raising the temperature of thedispersion of the synthesized mica particles to 60 to 100° C., theprecursor material of the metal oxides or the mixtures thereof are addedto the dispersion. For the precursor components of the metal oxidescoated according to the present invention, the examples of theprecursors of titanium dioxide are TiCl₄ (TiOCl₂ in an aqueoussolution), TiOSO₄ etc., and the examples of the precursors of iron oxideare FeCl₃, FeSO₄ and the like. The examples of the preferable metaloxides to be further added are SiCl₄, ZrOCl₂, SnCl₄, Na₂O, SiO₂.5H₂O,MnCl₂, MgCl₂, AlCl₃ and the like. Acidity of the dispersion in thecourse of adding the precursors is retained preferably at pH 1 to 4.Acid, preferably hydrochloric acid is added to the dispersion to adjustpH between 1 and 4, and a basic aqueous solution such as sodiumhydroxide is added thereto so that the hydrous titanium dioxide or ironoxide may be adsorbed on the base material by introduction of metaloxides precursors. In this process, it is important to titrate theprecursors of metal oxides while maintaining said pH range. When pH ofthe dispersion is less than 1, a hydrolysis is not taken place, and whenpH of the dispersion exceed 4, a hydrolysis is rapidly taken place andthereby causing the metal oxides not to be coated on the base materialand to be agglomerated each other. This coating method is well known bythe skilled in the art. Generally, a coating layer having anatasecrystal structure is formed when the coating layer of the hydrous metaloxide is formed on the synthesized mica as a base material, however, acoating layer having rutile crystal structure may be formed byprecoating the synthesized mica with tin dioxide (SnO₂) layer asdisclosed above. As the titration of the precursors proceeds, thecoating thickness of the hydrous metal oxide increases. The colors ofsilver, gold, red, purple, blue and green exhibit in proportion to thethickness. The synthesized mica coated as above is subjected tofiltration, washing with water, drying, calcination, and screening tomake final product in a mass production. The above processes after thecoating process is well known in the art.

In the mean time, the present invention provides a pearlescent pigmentprepared by adding a suitable surfactant prior to the coating process ofmetal oxide. Submicron-sized particles attached to the large particlesor overlapped each other are dispersed on account of repelling force atthe electrically charged interfaces of the synthesized mica by addingthe surfactant, thereby the pigment particles are prevented from beingagglomerated each other. Further, the interface of the synthesized micaand the interface of the hydrous metal oxide adsorbed to the basematerial by the hydrolysis are activated to allow smooth and stableadsorption. Particularly, when the hydrous metal oxides are not adsorbedon the base material and agglomerated by themselves to form the freeparticles, luster deteriorates and the amount of the metal oxideprecursors is more needed than actually required. Accordingly, theamount of the generated waste can be reduced and the cost for preparingthe pigment can be reduced by using a surfactant. The surfactant used inthe present invention is selected from cationic, anionic, nonionic oramphionic surfactants. Examples of the anionic surfactant include sodiumbistridecyl sulfosuccinate, sodium diisopropyl naphthalene sulfonate andthe like. Examples of the cationic surfactant includealkylamine-guanidine polyoxyethanol, etc. Examples of the nonionicsurfactant include sorbitan monooleate, etc. Examples of amphionicsurfactant include cocoamidopropyl betaine, etc. The surfactant whichcan be used in the present invention is not limited to the above listedones, various surfactants can be used as long as the present inventioncan be attained. Such use of the surfactant is advantageous in that thesynthesized mica particles ground by a water mixer as well as theconventional wet pulverizer can be used. 0.0001 to 1.0% by weight of thesurfactant is added to the dispersion of the synthesized mica, retainedfor 10 to 20 minutes, and then subjected to the coating process of themetal oxide.

The present invention is described in more detail by Examples andComparative Examples, but the Examples are only illustrative and,therefore, not intended to limit the scope of the present invention.

EXAMPLE 1

The synthesized mica (JED-1 manufactured by Jiafeng Co., Ltd.) wasground in a water mixer and then separated to three portions as averagesizes, 100 μm, 150 μm and 250 μm of the synthesized mica particles. 100g of the synthesized mica particles were added to and dispersed in 1liter of the deionized water, and then raised to the temperature of 60to 100° C. Thereafter, 5% hydrochloric acid was added thereto to lowerpH to 1 to 3, and refluxed for 10 minutes. 40% TiOCl₂ aqueous solution(a state TiCl₄ is soluted in water) was titrated and continued tomaintain said pH with sodium hydroxide. As the amount of TiOCl₂ to beadded is increased, the colors of silver, gold, red, blue and green wasexhibited, titration of TiOCl₂ was stopped upon obtaining the desiredcolor, refluxed for 10 minutes, and said solution was subjected tofiltration, washing and drying, and then calcined in an electric furnaceat the temperature of 700 to 1000° C. As a result of X-ray diffractionanalysis for the calcined pigment, it was confirmed that titaniumdioxide layer having anatase structure was formed on the surface of thesynthesized mica.

EXAMPLE 2

The synthesized mica used in Example 1 was ground in a water mixer andthen separated to three portions as average sizes, 100 μm, 150 μm and250 μm of the synthesized mica particles. 100 g of the synthesized micaparticles were added to and dispersed in 1 liter of the deionized water,and then raised to the temperature of 60 to 100° C. Thereafter, 5%hydrochloric acid was added thereto to lower pH to 1 to 3, and refluxedfor 10 minutes. 10 to 100 cc of 5% SnCl₄.n(H₂O) were added thereto andthen refluxed for 10 minutes. 40% TiOCl₂ aqueous solution was titratedand continued to maintain said pH with sodium hydroxide. Titration ofTiOCl₂ was stopped upon obtaining the desired color, refluxed for 10minutes, and said solution was subjected to filtration, washing anddrying, and then calcined in an electric furnace at the temperature of700 to 1000° C. As a result of X-ray diffraction analysis for thecalcined pigment, it was confirmed that titanium dioxide layer having arutile structure was formed on the surface of the synthesized mica.

EXAMPLE 3

The same procedure as in Example 1 was carried out except that 0.0001 to1% by weight of OS (sodium diisopropyl naphthalene sulfonate,manufactured by Cytec. Co., Ltd.) as an anionic surfactant was addedbefore titrating 40% TiOCl₂ aqueous solution to obtain the pearlescentpigment. It was confirmed that the synthesized mica particles coatedwith titanium dioxide layer were not agglomerated each other anduniformly dispersed in the obtained pigment, and that the titaniumdioxide layer was smoothly and uniformly formed on the surface of thebase material.

EXAMPLE 4

The same procedure as in Example 1 was carried out except that 0.0001 to1% by weight of C-61 (alkylamine-guanidine polyoxyethanol, manufacturedby Cytec. Co., Ltd.) as an anionic surfactant was added before titrating40% TiOCl₂ aqueous solution to obtain the pearlescent pigment. As isapparent in FIG. 2, it was confirmed that the synthesized mica particlescoated with titanium dioxide layer were not agglomerated each other anduniformly dispersed in the obtained pigment, and that the titaniumdioxide layer was smoothly and uniformly formed on the surface of thebase material.

EXAMPLE 5

The same procedure as in Example 1 was carried out except that 0.0001 to1% by weight of TR 70 (sodium bistridecyl sulfosuccinate, manufacturedby Cytec. Co., Ltd.) as an anionic surfactant was added before titrating40% TiCCl₂ aqueous solution to obtain the pearlescent pigment. It wasconfirmed that the synthesized mica particles coated with titaniumdioxide layer were not agglomerated each other and uniformly dispersedin the obtained pigment, and that the titanium dioxide layer wassmoothly and uniformly formed on the surface of the base material.

EXAMPLE 6

The same procedure as in Example 1 was carried out except that 0.0001 to1% by weight of Monopol SP-1 (Sorbitan monooleate, manufactured by DongNam Synthesis. Co., Ltd.) as an anionic surfactant was added beforetitrating 40% TiOCl₂ aqueous solution to obtain the pearlescent pigment.It was confirmed that the synthesized mica particles coated withtitanium dioxide layer were not agglomerated each other and uniformlydispersed in the obtained pigment, and that the titanium dioxide layerwas smoothly and uniformly formed on the surface of the base material.

EXAMPLE 7

The same procedure as in Example 1 was carried out except that 0.0001 to1% by weight of MITAINE CA (cocoamidopropyl betaine, manufactured byCytec. Co., Ltd.) as an anionic surfactant was added before titrating40% TiOCl₂ aqueous solution to obtain the pearlescent pigment. It wasconfirmed that the synthesized mica particles coated with titaniumdioxide layer were not agglomerated each other and uniformly dispersedin the obtained pigment, and that the titanium dioxide layer wassmoothly and uniformly formed on the surface of the base material.

EXAMPLE 8

The synthesized mica used in Example 1 was ground in a conventional wetpulverizer and then separated to average size 20 μm of the synthesizedmica particles. 80 g of the synthesized mica particles were dispersed in1 liter of deionized water, raised to the temperature of 60 to 100° C.,and then 0.0001 to 1% by weight of TR 70 (sodium bistridecylsulfosuccinate, manufactured by Cytec. Co., Ltd.) as an anionicsurfactant was added thereto. Thereafter, 5% hydrochloric acid was addedthereto to lower pH to 1 to 3, and refluxed for 10 minutes. 10 to 100 ccof 5% SnCl₄.n(H₂O) were added to the dispersion and then refluxed for 10minutes. 40% TiOCl₂ aqueous solution was titrated and continued tomaintain said pH with sodium hydroxide. Titration of TiOCl₂ was stoppedupon obtaining the desired color, refluxed for 10 minutes, and saidsolution was subjected to filtration, washing and drying, and thencalcined in an electric furnace at the temperature of 700 to 1000° C. Asa result of X-ray diffraction analysis for the calcined pigment, it wasconfirmed that titanium dioxide layer having rutile structure was formedon the surface of the synthesized mica.

EXAMPLE 9

The same procedure as in Example 1 was carried out except that thesynthesized mica ground in a water mixer was further pulverized in anedge runner mill, and separated to five portions as average particlesizes, 8 μm, 10 μm, 200 μm, 50 μm and 80 μm, of the synthesized micaparticles, and the obtained particles were coated with titanium dioxidelayer. As a result of X-ray diffraction analysis for the calcinedpigment, it was confirmed that titanium dioxide layer having anatasestructure was formed on the surface of the synthesized mica and thatluster was highly improved on account of more minute particles.

EXAMPLE 10

The same procedure as in Example 2 was carried out except that thesynthesized mica ground in a water mixer was further pulverized in anedge runner mill, and then separated to five portions as averageparticle sizes, 8 μm, 10 μm, 200 μm, 50 μm and 80 μm of the synthesizedmica particles, and the obtained particles were coated with titaniumdioxide layer. As a result of X-ray diffraction analysis for thecalcined pigment, it was confirmed that titanium dioxide layer havingrutile structure was formed on the surface of the synthesized mica andthat luster was highly improved on account of more minute particles.

EXAMPLE 11

The same procedure as in Example 3 was carried out except that thesynthesized mica ground in a water mixer was further pulverized in anedge runner mill, and then separated to five portions as averageparticle sizes, 80 μm, 10 μm, 20 μm, 50 μm and 80 μm of the synthesizedmica particles, and the obtained particles were coated with titaniumdioxide layer. As a result of X-ray diffraction analysis for thecalcined pigment, it was confirmed that titanium dioxide layer havinganatase structure was formed on the surface of the synthesized mica andthat the dispersibility among the particles was highly improved, andthus luster was excellent.

EXAMPLE 12

The same procedure as in Example 4 was carried out except that thesynthesized mica ground in a water mixer was further pulverized in anedge runner mill, and then separated to five portions as averageparticle sizes, 80 μm, 10 μm, 20 μm, 50 μm and 80 μm of the synthesizedmica particles, and the obtained particles were coated with titaniumdioxide layer. As a result of X-ray diffraction analysis for thecalcined pigment, it was confirmed that titanium dioxide layer havingrutile structure was formed on the surface of the synthesized mica andthat the dispersibility among the particles was highly improved, andthus luster was excellent.

COMPARATIVE EXAMPLE 1

The same procedure as in Example 1 was carried out except that thesynthesized mica “JED-1” (manufactured by Jiafeng Co., Ltd.) was groundin an edge runner mill and then separated to three portions as averageparticle sizes, 100 μm, 150 μm and 250 μm of the synthesized mica toobtain pearlescent pigment. As is apparent in FIGS. 3 and 4, it wasconfirmed that the synthesized mica particles in the obtained pigmentswere agglomerated each other, and that the titanium dioxide layer wasnot uniformly formed on the surface of the base material.

COMPARATIVE EXAMPLE 2

The same procedure as in Comparative Example 1 was carried out exceptthat the synthesized mica particles having average particle sizes, 80μm, 10 μm, 20 μm, 50 μm and 80 μm were obtained by using an edge runnermill, and then the particles were coated with titanium dioxide layer toobtain pearlescent pigments. The obtained pigments were better in lusterand chroma than those obtained in Comparative Example 1, however thesynthesized mica particles were slightly agglomerated each other, andthe titanium dioxide layer was not satisfactory in flatness.

EXAMPLE 13 Evaluation of Luster and Chroma

The luster and chroma of the pearlescent pigments prepared in Examples 1to 4 and Comparative Example 1 were evaluated as follows and the resultswere shown in Table 1, below. The evaluation was commenced by mixing anitrocellulose solution having a viscosity of 1,200 cps with apearlescent pigment (weight ratio of 94:6) by using a mixing bar,letting a certain amount of the mixture fall on a draw down card (D.Dcard) at the same place as ST sample, drawing down the mixture from theabove-obtained card onto a concealing rate measure paper printed withblack and white colors by use of a doctor blade, and drying it in theair. The luster and chroma were evaluated with naked eyes.

TABLE 1 Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 1 Luster ⊚ ⊚ ⊚ ⊚ Δ Chroma ⊚ ⊚⊚ ⊚ Δ Δ: usual ⊚: very good

EXAMPLE 14 Evaluation of Luster and Chroma

The luster and chroma of the pearlescent pigments prepared in Examples 8to 12 and Comparative Example 2 were evaluated as follows and theresults were shown in Table 2, below. The evaluation was commenced bymixing a nitrocellulose solution having a viscosity of 1,200 cps with apearlescent pigment (weight ratio of 94:6) by using a mixing bar,letting a certain amount of the mixture fall on a draw down card (D.Dcard) at the same place as ST sample, drawing down the mixture from theabove-obtained card onto a concealing rate measure paper printed withblack and white colors by use of a doctor blade, and then drying it inthe air. The luster and chroma were evaluated with naked eyes.

TABLE 2 Comp. Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 2 Luster ⊚ ⊚ ⊚ ⊚ ⊚ ◯Chroma ⊚ ⊚ ⊚ ⊚ ⊚ ◯ ◯: good ⊚: very good

EXAMPLE 15 Evaluation on Surfactant's Effect

The luster, chroma and dispersibility of the pearlescent pigmentsprepared in Examples 3 to 7 and Comparative Example 1 were evaluated asfollows. The luster and chroma of the pearlescent pigment were evaluatedin a same manner as Examples 13 and 14, and the dispersibility of thepearlescent pigment was evaluated by comprehensively considering luster,chroma, shielding property and the like. The results were shown in Table3, below.

TABLE 3 Comp. Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 1 Luster ⊙ ⊙ ⊙ ⊙ ⊙ ◯Chroma ⊙ ⊙ ⊙ ⊙ ⊙ ◯ Dispersibility ⊙ ⊙ ⊙ ⊙ ⊙ ◯ ◯: good ⊙: extremely good

INDUSTRIAL APPLICABILITY

According to the present invention, the synthesized mica as basematerial is ground in a water mixer to make the obtained particlessmooth, to uniformly and smoothly coat metal oxides, and thus to obtainthe pearlescent pigment having excellent luster and chroma. Further, thesurfactant may be added to the synthesized mica ground by using a watermixer and/or a conventional wet pulverizer, and the obtained synthesizedmica may be coated with metal oxides, and thereby attaining an excellentdispersibility of the particles and smooth coating layer.

The present invention being thus described, it will be obvious that thesame may be varied in many ways. Such variations are not to be regardedas a departure from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A method for preparing a pearlescent pigment by coating metal oxideson the synthesized mica, comprising the steps of: (1) grinding thesynthesized mica by agitating the mica with water in a wet pulverizer toa particle size between 5 and 500 μm and separating the mica; (2)dispersing the separated particles of the synthesized mica in water andadding 0.0001 to 1.0% by weight of cationic, anionic, nonionic oramphionic surfactant thereto; (3) adding acid to the dispersioncontaining the surfactant to adjust pH between 1 and 4; (4) adding themetal oxide precursors and the basic aqueous solution thereto whilemaintaining said pH range until the desired color is attained, andthereby forming at least one hydrous metal oxides layers on theparticles of the synthesized mica; and (5) filtering, water-washing,drying and calcining the synthesized mica coated with the metal oxideslayers.
 2. A method for preparing a pearlescent pigment by coating metaloxides on the synthesized mica, comprising the steps of: (1) grindingthe synthesized mica by agitating the mica with water in a water mixerto a particle size between 100 and 500 μm and separating the mica; (2)dispersing the separated particles of the synthesized mica in water andadding 0.0001 to 1.0% by weight of cationic, anionic, nonionic oramphionic surfactant thereto; (3) adding acid to the dispersioncontaining the surfactant to adjust pH between 1 and 4; (4) adding themetal oxide precursors and the basic aqueous solution while maintainingsaid pH range until the desired color is attained, and thereby formingat least one hydrous metal oxides layers on the particles of thesynthesized mica; and (5) filtering, water-washing, drying and calciningthe synthesized mica coated with the metal oxides layers.
 3. The methodfor preparing a pearlescent pigment as set forth in claim 2, wherein themetal oxide comprises one or more than two metal oxides.
 4. The methodfor preparing a pearlescent pigment as set forth in claim 3, wherein themetal oxide layer is titanium dioxide (TiO₂) layer, iron oxide (Fe₂O₃)layer, or the combination thereof.
 5. The method for preparing apearlescent pigment as set forth in claim 3, wherein the metal oxidelayer comprises a main metal oxide component and an assistant metaloxide component, the main metal oxide component being selected from thegroup consisting of titanium dioxide (TiO₂), iron oxide (Fe₂O₃) and amixture thereof, and the assistant metal oxide component being selectedfrom the group consisting of tin dioxide (SnO₂), zirconium dioxide(ZrO₂), silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), magnesium oxide(MgO), manganese dioxide (MnO₂) and a mixture thereof.
 6. The method forpreparing a pearlescent pigment as set forth in claim 2, furthercomprising a step of re-coating the calcined pigment particles with ametal oxide selected from the group consisting of chromium, zirconium,aluminum and a mixture thereof or treated with silane.
 7. The method forpreparing a pearlescent pigment as set forth in claim 1, wherein theanionic surfactant is sodium bistridecyl sulfosuccinate or sodiumdiisopropyl naphthalene sulfonate; the cationic surfactant isalkylamine-guanidine polyoxyethanol; the nonionic surfactant is sorbitanmonooleate; and the amphionic surfactant is cocoamidopropyl betaine. 8.The method for preparing a pearlescent pigment as set forth in claim 2,wherein the grinding step of the synthesized mica is carried out byintroducing water and the synthesized mica in the water mixer at aweight ratio of 10:1 to 1:1, and agitating them at the revolution speedof 100 to 1000 rpm for 0.5 to 2 hours.
 9. The method for preparing apearlescent pigment as set forth in claim 2, further comprising a stepof pulverizing the particles of the synthesized mica to a size of 5 to100 μm with a wet pulverizer after grinding the synthesized mica withthe water mixer.
 10. The method for preparing a pearlescent pigment asset forth in claim 1, wherein the metal oxide layer comprises one ormore than two metal oxides.
 11. The method for preparing a pearlescentpigment as set forth in claim 2, wherein the anionic surfactant issodium bistridecyl sulfosuccinate or sodium diisopropyl naphthalenesulfonate; the cationic surfactant is alkylamine-guanidinepolyoxyethanol; the nonionic surfactant is sorbitan monooleate; and theamphionic surfactant is cocoamidopropyl betaine.